drivers: eth: gmac: Implement the get_config callback
drivers: eth: gmac: Implement the get_config callback

Handle getting the number of priority queues. The total number of queues
for this driver is configured in kconfig so it is as simple as returning
a defined value in this case.

Signed-off-by: Tomasz Gorochowik <265c7c25eca9aa9127910457b0aea7e793d329f1@antmicro.com>

ldts/zephyr,explora26/zephyr,nashif/zephyr,punitvara/zephyr,nashif/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,kraj/zephyr,explora26/zephyr,kraj/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,explora26/zephyr,punitvara/zephyr,ldts/zephyr,finikorg/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,kraj/zephyr,finikorg/zephyr,finikorg/zephyr,punitvara/zephyr,galak/zephyr,kraj/zephyr,galak/zephyr,Vudentz/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,Vudentz/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,Vudentz/zephyr,ldts/zephyr,finikorg/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,Vudentz/zephyr,Vudentz/zephyr,nashif/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,kraj/zephyr,nashif/zephyr